Beta receptor antagonists in the treatment of heart failure

Dobutamine-induced hypotension is an independent predictor for mortality in patients with left ventricular dysfunction following myocardial infarction

Dobutamine echocardiography was performed on 297 patients after acute myocardial infarction to assess the prognostic value of dobutamine-induced hypotension in patients with left ventricular dysfunction. Patients were divided into two groups according to ejection fraction (group I, ejection fraction <0.45, n = 123; group II, ejection fraction > or =0.45, n = 174) and were followed for 20+/-8 months. Hypotension was defined as a decrease in systolic blood pressure > or =20 mm Hg, compared with baseline values. The incidence of hypotension was similar in groups I and II (23.6% vs. 18.4%, P = 0.28), and the hypotension was not related to positive dobutamine echocardiography. Univariate analysis showed that the development of hypotension was associated with a higher incidence of cardiac death in group I but not in group II. Multivariate analysis showed that dobutamine-induced hypotension was an independent predictor only for cardiac death in group I and was not related to any other cardiac events in either group. In conclusion, the development of hypotension during dobutamine stress can identify a subgroup with poor ventricular functional reserve and at high risk for cardiac death among patients complicated with left ventricular dysfunction.

Current and newer approaches in the drug treatment of congestive heart failure

Most patients with chronic congestive heart failure (CHF) are subjected to symptomatic treatment, predominantly with drugs. Over the years, it has become clear that treatment with unloading drugs is probably more beneficial than treatment with inotropic agents. In addition, it has been widely recognized that the neuroendocrine compensatory changes associated with CHF afford and important target for drug treatment. This may also hold for some of the changes in receptor density, such as the downregulation of cardiac beta-adrenoceptors. The present and clearly changing insights into the backgrounds of drugs for the treatment of CHF are critically discussed. Apart from the changing views and appreciation of the currently used drugs (diuretics, ACE inhibitors, digoxin, beta-adrenoceptor agonists), the following new approaches are discussed: beta-blockers, angiotensin II receptor antagonists, ibopamine, calcium antagonists, inhibitors of ANP degradation, vasopression antagonist, vesnarinone, and calcium sensitizers.

Pharmacologic characterization in vitro and in vivo of iodine 123-labeled derivatives of the beta-adrenoceptor antagonist CGP12177, designed for the imaging of cardiac beta-receptors

BACKGROUND

Potential new radioligands for the noninvasive imaging of cardiac beta-adrenoceptors with single-photon emission computed tomography were investigated.

METHODS AND RESULTS

Two iodinated derivatives of CGP12177 para (S-CYBL2B) and ortho (CYBL2A) substituted CGP12177 and an iodinated form of nadolol (CYBL1) were synthesized. Their affinity was tested in vitro (left ventricular homogenates). The biodistribution of [123I]S-CYBL2B was evaluated in rabbits. Specific binding was assessed by pretreatment of the animals with 0.1 mumol propranolol. The inhibition constant values (in nanomolars, means +/- SEM; n = 3 to 5) were determined at 1.17 +/- 0.42, 28800 +/- 9260, 11.1 +/- 2.1, 53.0 +/- 19.9, and 1790 +/- 700 for CGP12177, CYBL2A, S-CYBL2B, nadolol, and CYBL1. Myocardial uptake of [123I]S-CYBL2B was not inhibited by pretreatment of the animals with propranolol, but uptake by lung tissue could be blocked by propranolol (0.63% +/- 0.09% vs 0.33% +/- 0.02% % injected dose/g x kg; p < 0.05). In isolated right atria, preincubation with S-CYBL2B induced a parallel rightward shift of the concentration-response curve with isoprenaline.

CONCLUSIONS

S-CYBL2B shows high affinity for cardiac beta-adrenoceptors, but binding proved nonspecific in vivo, whereas binding in lung tissue was specific. These results suggest that S-CYBL2B is probably not a suitable radioligand for receptor imaging.

Use of beta-adrenoceptor blockers in patients with congestive heart failure

The beneficial effect of chronic beta-blockade in patients with congestive heart failure has been repeatedly shown since its introduction into treatment for this condition in 1975. Still this kind of therapy remains controversial, it is sometimes regarded as a therapeutic paradox, and its use is mainly limited to specialist centers. Various favorable effects of beta-blockers in patients with heart failure due to idiopathic dilated cardiomyopathy and ischemic heart disease have been demonstrated, the principal among them being reduction in energy requirements and ischemia, antiarrhythmogenic effect, improvement of diastolic function, protection of myocytes against catecholamine overload, centrally mediated increase in vagal tone, upregulation of beta-adrenergic receptors, and possible blockade of autoantibodies against beta 1-receptors. Although most of the studies used metoprolol, these effects may be relevant to certain other beta-blockers. Despite very solid pathophysiological and pharmacological rationales for the use of beta-blockade, a major obstacle for a general acceptance of this therapeutic concept is the striking contrast between hemodynamic changes during the acute effect and long-term treatment. When titrated carefully from very low doses and used with a true commitment to long-term treatment, beta-blockers have been shown to prevent further deterioration of heart failure and to improve hemodynamics, exercise tolerance, quality of life, and prognosis.

Pharmacotherapy of congestive heart failure. Currently used and experimental drugs

A survey is given of the currently used therapeutics in the treatment of chronic congestive heart failure. Symptomatic treatment is usually performed along the following lines: rest, sodium and fluid restriction to unload the decompensating heart, loop diuretics, angiotensin-converting enzyme inhibitors or other vasodilators; inotropic agents to improve the heart's mechanical performance; attempts to counteract the neuro-endocrine compensatory mechanisms, that is the activated sympathetic nervous and renin-angiotensin-aldosterone systems, as well as the rise in vasopressine levels. New insights have been obtained in the effects of cardiac glycosides, which are probably rather based on counteracting the elevated sympathetic neuronal activity than on their weak and uncertain inotropic action. Angiotensin-converting enzyme inhibitors are probably more effective than classical vasodilators owing to their additional interaction with the neuro-endocrine compensatory mechanisms. Ibopamine, a prodrug of epinine, appears to be rather a vasodilator and antagonist of the neuro-endocrine compensatory mechanisms than an inotropic agent. The most important clinical trials addressing the efficacy and adverse reactions to the various aforementioned therapeutics are discussed. New, experimental approaches in the drug treatment of chronic congestive heart failure include beta-blockers, calcium antagonists, vasopressin antagonists and inhibitors of atrial natriuretic peptide degradation.

Pathophysiologic and pharmacologic rationales for clinical management of chronic heart failure with beta-blocking agents

An understanding of the important role of neurohormonal compensatory mechanisms in heart failure has been translated into therapeutic options that can improve cardiac function, alter disease progression, and improve survival. Angiotensin-converting enzyme inhibitors are of proven benefit in this regard, and beta-adrenergic receptor antagonists are potentially another such class of agents. By inhibiting the myocardial effects of chronic adrenergic activation, beta blocking agents may improve left ventricular function or delay its deterioration in patients with heart failure. Aside from blocking beta-adrenergic receptors, other ancillary properties inherent in third-generation beta-blocking agents (such as vasodilation) may exert additional favorable effects. Clinical data generated in subjects with heart failure indicate that beta-antagonist therapy exerts its physiologic and clinical effects through neurohormonal antagonism, generally analogous to angiotensin-converting enzyme inhibitors. Virtually all controlled long-term studies show that beta-blocking agents improve cardiac function and hemodynamics in patients with chronic heart failure, but large-scale trials are needed to ascertain a favorable effect on the natural history of heart failure.